1. Field of the Invention
The present invention relates to a multilayer capacitor built-in substrate.
2. Description of the Related Art
In recent years, as the performance of electronic devices has been increased, the capacitance of multilayer ceramic capacitors has been increased progressively.
In the case of high-capacitance multilayer ceramic capacitors, high dielectric constant ceramic materials such as barium titanate, have been used as a dielectric material.
These high dielectric constant ceramic materials include piezoelectric and electrostrictive properties, and thus, in multilayer ceramic capacitors including dielectrics composed of the high dielectric constant ceramic materials, mechanical distortion will be produced when a voltage is applied.
Therefore, when an alternating-current voltage or a direct-current voltage with an alternating-current component superimposed thereon is applied to the multilayer ceramic capacitors mounted on circuit boards, vibrations will be generated in the multilayer ceramic capacitor due to distortion of the multilayer ceramic capacitors, and the vibrations will propagate to the circuit boards, thereby vibrating the circuit boards.
In this regard, when the circuit board vibrates at a frequency of 20 Hz to 20,000 Hz in the audible frequency range due to the propagated vibration, noise referred to as “acoustic noise” will be generated.
Various proposals have been made as techniques to reduce the noise described above. For example, in the multilayer ceramic capacitor described in Japanese Patent Application Laid-Open No. 2015-65414, a capacitor main body integrally includes a capacitance part, an upper protection part, and a lower protection part, and the thickness of the lower protection part is larger than the thickness of the upper protection part so that the capacitance part is positioned on the upper side in the height direction of the capacitor main body. In addition, in the multilayer ceramic capacitor described in Japanese Patent Application Laid-Open No. 2015-226026, a capacitor main body includes a first protection part, a capacitance part, an electrostrictive relaxation part, a characteristic adjustment part, and a second protection part provided in layers in the height direction, and when the thickness of the capacitance part, the thickness of the electrostrictive relaxation part, and the thickness of the characteristic adjustment part are denoted respectively by T2, T3, and T4, the condition of T2>T3>T4 is satisfied. Furthermore, in the multilayer ceramic capacitor described in Japanese Patent Application Laid-Open No. 2016-127045, a capacitor main body includes a first protection part, a capacitance part, and a second protection part provided in layers in this order in the height direction, the capacitor part includes a high capacitance part and a low capacitance part continuously in the height direction, and the opposed interval between n2 layers of internal electrode layers included in the low capacitance part is larger than the opposed interval between n1 layers of internal electrode layers included in the high capacitance part.
In recent years, electronic component built-in substrates have been proposed in which electronic components such as, multilayer ceramic capacitors, are buried in the substrates, thereby achieving reductions in substrate thickness. However, when the multilayer ceramic capacitors described in Japanese Patent Application Laid-Open No. 2015-65414, Japanese Patent Application Laid-Open No. 2015-226026, and Japanese Patent Application Laid-Open No. 2016-127045 are mounted on substrates, and the multilayer ceramic capacitors are buried in burying layers including a resin, the burying layers are also believed to propagate distortion of the multilayer ceramic capacitors to the substrates. As a result, there is a concern that the vibrations of the substrates will be increased, thereby making it difficult to suppress acoustic noise.